Multiple chemistry electrochemical plating method

ABSTRACT

Embodiments of the invention generally include a method and intermediate plating solution for plating metal onto a substrate surface. The method generally includes filling the features and/or growing a film layer on the field areas by plating a metal from a first solution on a seed layer under an applied first current, wherein the first solution includes an acid in an amount sufficient to provide a first solution pH of about 6 or less, copper ions, and at least one suppressor. The method may further include substantially filling features by plating metal ions from a second solution onto the substrate under an applied second current to form a metal layer, wherein the second solution includes an acid in an amount sufficient to provide a second solution pH of from about 0.6 to about 3, copper ions, at least one suppressor and at least one accelerator and growing a film layer on the field areas by contacting the metal layer with a third solution under an applied third current, wherein the third solution includes an acid, copper ions, at least one suppressor, at least one accelerator and at least one leveling agent. The intermediate plating solution generally includes copper sulfate in a concentration of from about 5 g/L to about 50 g/L, sulfuric acid in a concentration sufficient to provide a pH of less than about 6 and suppressors having a molecular weight of 600 or greater.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of U.S. Provisional PatentApplication Serial No. 60/436,180, filed Dec. 24, 2002, and U.S.Provisional Patent Application Serial No. 60/510,190, filed Oct. 10,2003. Both of the above applications are hereby incorporated byreference in their entireties.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] Embodiments of the invention generally relate to a multiplechemistry electrochemical plating method.

[0004] 2. Description of the Related Art

[0005] Metallization for sub-quarter micron sized features is afoundational technology for present and future generations of integratedcircuit manufacturing processes. In devices such as ultra large scaleintegration-type devices, i.e., devices having integrated circuits withmore than a million logic gates, the multilevel interconnects that lieat the heart of these devices are generally formed by filling highaspect ratio interconnect features with a conductive material, such ascopper or aluminum, for example. Conventionally, deposition techniquessuch as chemical vapor deposition (CVD) and physical vapor deposition(PVD), for example, have been used to fill these interconnect features.However, as interconnect sizes decrease and aspect ratios increase,void-free interconnect feature fill via conventional metallizationtechniques becomes increasingly difficult. As a result thereof, platingtechniques, such as electrochemical plating (ECP) and electrolessplating, for example, have emerged as viable processes for fillingsub-quarter micron sized high aspect ratio interconnect features inintegrated circuit manufacturing processes.

[0006] In an ECP process, for example, sub-quarter micron sized highaspect ratio features formed into the surface of a substrate may beefficiently filled with a conductive material, such as copper. ECPplating processes are generally two stage processes, wherein a seedlayer is first formed over the surface features of the substrate (thisprocess may be performed in a separate system), and then the surfacefeatures of the substrate are exposed to an electrolyte solution whilean electrical bias is simultaneously applied between the substrate andan anode positioned within the electrolyte solution. The electrolytesolution is generally rich in ions to be plated onto the surface of thesubstrate. Therefore, the application of the electrical bias causesthese ions to be urged out of the electrolyte solution and to be platedonto the seed layer.

[0007] One challenge associated with conventional ECP processes is thatthe supporting hardware, i.e., the electrochemical plating systems, arelimited to a single chemistry for use in the electrochemical platingprocess. The availability of a single chemistry presents challenges toplating processes, as the single chemistry must be used to accomplishseveral very different plating processes. For example, the singlechemistry may be used to deposit a seed layer over a barrier layer, todeposit a feature filling layer, to deposit a bulk fill layer, todeposit a metal alloy layer, to deposit an adhesion layer, or any otherlayer known in the electrochemical plating art. The challenge with usinga single chemistry for more than one plating process is that the singlechemistry is generally not able to provide the best characteristics foreach plating process. For example, a chemistry configured to deposit afeature fill layer would have different characteristics and chemicalcompositions than a chemistry configured to deposit a bulk fill layer.The feature fill layer is generally plated much slower than a bulk filllayer and a primary concern with the feature fill layer is notprematurely closing off the openings of high aspect ratio features beingfilled, wherein the bulk fill deposition is a much faster depositionprocess that is not concerned with the throat closure. Thus, conductingboth steps from a single chemistry requires balancing of severalparameters, which inherently sacrifices some of the advantageouscharacteristics of the respective processes.

[0008] Another example of a plating process where a multiple chemistrysystem would have advantages over a single chemistry system is a directplating on barrier layer (rubidium, cobalt, tantalum nitride, or othermetal known to be an acceptable electrochemical plating barrier layer)plating processes. In this configuration a first chemistry could beconfigured to plate a layer directly on the barrier layer with adequateadhesion to support a subsequent layer plated thereon with a secondchemistry configured to optimize the subsequent layer. Yet anotherexample of an advantage provided by a multiple chemistry plating methodis a plating process where a first plating chemistry may be configuredto be highly resistive (more resistive than a thin seed layer), so thatthe chemistry can effectively plate on the thin seed layer withouthaving edge high plating problems. Then a second chemistry that is lessresistive may be used to continue plating at a much higher depositionrate than the resistive chemistry. Yet another example of an advantageprovided by a multiple chemistry plating method is a process wheremultiple chemistries are used to plate a combination of alloy andgenerally pure metal layers, such as a copper alloy followed by agenerally pure copper layer or a generally pure layer followed by acopper alloy layer.

[0009] Although a multi-chemistry plating process is desirable, systemmanufacturers have not been able to develop a multi-chemistry system.This is generally a result of the challenges (plumbing, isolation, spacerequirements, etc.) associated with providing multiple chemistries to asingle electrochemical plating system. Space requirements are a primaryfactor limiting implementation of an ECP system having multiplechemistries, as conventional plating systems generally include a large(over 200 liters) tank that supplies electrolyte to one or more platingcells on the plating system. Thus, for each additional chemistryprovided, an additional 200 liter tank would also have to be provided.Further, each tank of electrolyte is dosed with additives configured tocontrol plating parameters, and these additives would also have to bedosed into the second tank, which again increases the hardware, space,and consumption requirements. Further still, plating solutions are knownto deplete additives during the plating process, and although thesolutions can be periodically dosed to increase the concentrations ofthe depleted additives, the solutions nevertheless accumulate additivebreakdown products. As a result thereof, the entire solution must beperiodically discarded and replaced with a new solution void ofbreakdown products, which is costly in view of the large volume to bereplaced.

[0010] Therefore, in view of the challenges and limitations of singlechemistry plating processes, there is a need for a method for platingmetals onto a semiconductor substrate, wherein the method is capable ofutilizing multiple chemistries in a single plating system.

SUMMARY OF THE INVENTION

[0011] In one embodiment of the invention a plating method generallyincludes plating metal ions from a first plating solution onto asubstrate having features and field areas under a first applied current,wherein the first plating solution includes an acid in an amountsufficient to provide a first solution pH of about 7 or less, copperions, and at least one suppressor. Generally, pH in the range of about0.5 to about 3 corresponds to solutions containing primarily simple Cuions, whereas a pH in the range of about 3 to about 7 corresponds tosolutions generally containing complexed Cu ions where the complexingaction is provided by complexing agents, such as citric acid or tartaricacid, for example. The process includes plating metal ions from a secondplating solution onto the substrate under a second applied current tosubstantially fill the features, wherein the second plating solutionincludes an acid in an amount sufficient to provide a second solution pHof from about 0.6 to about 3, copper ions, at least one suppressor, andat least one accelerator. The process may further include plating metalions from a third plating solution onto the substrate under a thirdapplied current to ensure a substantially uniform fill of the features,wherein the third plating solution includes an acid, copper ions, atleast one suppressor, at least one accelerator and at least one levelingagent.

[0012] Embodiments of the invention may further provide an intermediateplating solution for plating a metal on a metal seed layer. Theintermediate plating solution generally includes copper sulfate in aconcentration of from about 5 g/L to about 50 g/L, sulfuric acid in aconcentration sufficient to provide a pH of less than about 6 andsuppressors having a molecular weight of 600 or greater.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] So that the manner in which the above-recited features of thepresent invention are obtained may be understood in detail, a moreparticular description of the invention briefly summarized above may behad by reference to the embodiments thereof, which are illustrated inthe appended drawings. It is to be noted, however, that the appendeddrawings illustrate only exemplary embodiments of the invention., andare therefore, not to be considered limiting of its scope, for theinvention may admit to other equally effective embodiments.

[0014]FIG. 1 is a top plan view of an embodiment of an electrochemicalprocessing system capable of implementing the method of the invention.

[0015]FIG. 2 illustrates a schematic diagram of a fluid supply system ofthe invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016]FIG. 1 is a top plan view of an embodiment of an electrochemicalprocessing system (ECP) 100 capable of implementing the methodology ofthe present invention. ECP system 100 generally includes a processingbase 113 having a robot 120 centrally positioned thereon. The robot 120generally includes one or more robot arms 122, 124 configured to supportsubstrates thereon. Additionally, the robot 120 and the accompanyingblades 122, 124 are generally configured extend, rotate, and verticallymove so that the robot 120 may insert and remove substrates to and froma plurality of processing cells 102, 104, 106, 108, 110, 112, 114, 116positioned on the base 113. Processing cells may be configured aselectrochemical plating cells, electroless plating cells, substraterinsing and/or drying cells, substrate bevel clean cells, substratesurface clean or preclean cells, and/or other processing cells that areadvantageous to plating processes.

[0017] ECP system 100 further includes a factory interface (FI) 130. FI130 generally includes at least one FI robot 132 positioned adjacent aside of the FI that is adjacent the processing base 113. This positionof robot 132 allows the robot to access substrate cassettes 134 toretrieve a substrate 126 therefrom and then deliver the substrate 126 toone of processing cells 114, 116 to initiate a processing sequence.Similarly, robot 132 may be used to retrieve substrates from one of theprocessing cells 114, 116 after a substrate processing sequence iscomplete. In this situation robot 132 may deliver the substrate 126 backto one of the cassettes 134 for removal from the system 100.Additionally, robot 132 is also configured to access an anneal chamber135 positioned in communication with FI 130. The anneal chamber 135generally includes a two position annealing chamber, wherein a coolingplate or position 136 and a heating plate or position 137 are positionedadjacently with a substrate transfer robot 140 positioned proximatethereto, e.g., between the two stations. The robot 140 is generallyconfigured to move substrates between the respective heating 137 andcooling plates 136.

[0018]FIG. 2 is a schematic diagram of one embodiment of the platingsolution delivery system 111. The plating solution delivery system 111is generally configured to supply a plating solution to each processinglocation on system 100 that requires the solution. More particularly,the plating solution delivery system is further configured to supply adifferent plating solution or chemistry to each of the processing cells.For example, the delivery system may provide a first plating solution orchemistry to processing cells 110, 112, while providing a differentplating solution or chemistry to processing cells 102, 104. Theindividual plating solutions are generally isolated for use with asingle plating cell, and therefore, cross contamination issues areminimized. However, embodiments of the invention contemplate that morethan one cell may share a common chemistry that is different fromanother chemistry that is supplied to another plating cell on thesystem. These features are advantageous, as the ability to providemultiple chemistries to a single processing platform allows for multiplechemistry plating processes on a single platform.

[0019] In another embodiment of the invention, a first plating solutionand a separate and different second plating solution can be providedsequentially to a single plating cell. Typically, providing two separatechemistries to a single plating cell requires the plating cell to bedrained and/or purged between the respective chemistries, however, inmany cases a mixed ratio of less than about 10 percent first platingsolution to the second plating solution is not be detrimental to filmproperties.

[0020] The plating solution delivery system 111 typically includes aplurality of additive sources 302 and at least one electrolyte source304 that are fluidly coupled to each of the processing cells of system100 via a manifold 332. Typically, the additive sources 302 include anaccelerator source 306, a leveler source 308, and a suppressor source310. The accelerator source 306 is adapted to provide an acceleratormaterial that typically adsorbs on the surface of the substrate andlocally accelerates the electrical current at a given voltage where theyadsorb. Examples of accelerators include sulfide-based molecules. Theleveler source 308 is adapted to provide a leveler material thatoperates to facilitate planar plating. Examples of levelers are nitrogencontaining long chain polymers. The suppressor source 310 is adapted toprovide suppressor materials that tend to reduce electrical current atthe sites where they adsorb (typically the upper edges/corners of highaspect ratio features). Therefore, suppressors slow the plating processat those locations, thereby reducing premature closure of the featurebefore the feature is completely filled and minimizing detrimental voidformation. Examples of suppressors include polymers of polyethyleneglycol, mixtures of ethylene oxides and propylene oxides, or copolymersof ethylene oxides and propylene oxides.

[0021] To minimize the amount of additives in consumed/wasted in platingprocesses, and more particularly, to prevent situations where anadditive source runs out and the system is not being supplied with aparticular additive, each of the additive sources 302 generally includesa bulk or larger storage container coupled to a smaller shot-typecontainer 316. The shot container 316 is generally filled from the bulkstorage container 314, and therefore, the bulk container may be removedfor replacement without affecting the operation of the fluid deliverysystem, as the associated shot container may supply the particularadditive to the system while the bulk container is being replaced.

[0022] In the embodiment depicted in FIG. 2, a dosing pump 312 iscoupled between the plurality of additive sources 302 and the pluralityof processing cells. The dosing pump 312 generally includes at least afirst through fourth inlet ports 322, 324, 326, 328. As an example, thefirst inlet port 322 is generally coupled to the accelerators source306, the second inlet port 324 is generally coupled to the levelersource 308, the third inlet port 326 is generally coupled to thesuppressor source 310, and the fourth inlet port 328 is generallycoupled to the electrolyte source 304. An output 330 of the dosing pump312 is generally coupled to the processing cells via manifold 332 by anoutput line 340 wherein mixing of the sequentially supplied additives(i.e., at least one or more accelerators, levelers and/or suppressors)may be combined with electrolyte provided to the manifold 332 through afirst delivery line 350 from the electrolyte source 304, to form thefirst or second plating solutions as desired. The dosing pump 312 may beany metering device(s) adapted to provide measured amounts of selectiveadditives to the process cells 102, 104. The dosing pump 312 may be arotary metering valve, a solenoid metering pump, a positive displacementpump, a diaphragm pump, a peristaltic pump, or other fluid meteringdevice acceptable for flowing electrochemical plating solutions to aplating cell. In one embodiment, the dosing pump includes a rotating andreciprocating ceramic piston that drives 1.00 ml per cycle of apredetermined additive.

[0023] In another embodiment of the invention the fluid delivery systemmay be configured to provide a second completely different platingsolution and associated additives. For example, in this embodiment adifferent base electrolyte solution (similar to the solution containedin container 304) may be implemented to provide the processing system100 with the ability, for example, to use plating solutions from twoseparate manufacturers. Further, an additional set of additivecontainers may also be implemented to correspond with the second baseplating solution. Therefore, this embodiment of the invention allows fora first chemistry (a chemistry provided by a first manufacturer) to beprovided to one or more plating cells of system 100, while a secondchemistry (a chemistry provided by a second manufacturer) is provided toone or more plating cells of system 100. Each of the respectivechemistries will generally have their own associated additives, however,cross dosing of the chemistries from a single additive source or sourcesis not beyond the scope of the invention.

[0024] In order to implement the fluid delivery system capable ofproviding two separate chemistries from separate base electrolytes, aduplicate of the fluid delivery system illustrated in FIG. 2 isconnected to the processing system. More particularly, the fluiddelivery system illustrated in FIG. 2 is generally modified to include asecond set of additive containers 302, a second pump assembly 330, and asecond manifold 332 (shared manifolds are possible). Additionally,separate sources for virgin makeup solution/base electrolyte 304 arealso provided. The additional hardware is set up in the sameconfiguration as the hardware illustrated in FIG. 2, however, the secondfluid delivery system is generally in parallel with the illustrated orfirst fluid delivery system. Thus, with this configuration implemented,either base chemistry with any combination of the available additivesmay be provided to any one or more of the processing cells of system100.

[0025] The manifold 332 is typically configured to interface with a bankof valves 334. Each valve of the valve bank 334 may be selectivelyopened or closed to direct fluid from the manifold 332 to the firstprocess cell 102 and/or the second process cell 104. The manifold 332and valve bank 334 may optionally be configured to support selectivefluid delivery to additional number of process cells. In the embodimentdepicted in FIG. 2, the manifold 332 and valve bank 334 include a sampleport 336 that allows different combinations of chemistries or componentthereof utilized in the system 100 to be sampled without interruptingprocessing.

[0026] In some embodiments, it may be desirable to purge the dosing pump312, output line 340 and/or manifold 332. To facilitate such purging,the plating solution delivery system 111 is configured to supply atleast one of a cleaning and/or purging fluid. In the embodiment depictedin FIG. 2, the plating solution delivery system 111 includes a deionizedwater source 342 and a non-reactive gas source 344 coupled to the firstdelivery line 350. The non-reactive gas source 344 may supply anon-reactive gas, such as an inert gas, air or nitrogen through thefirst delivery line 350 to flush out the manifold 332. Deionized watermay be provided from the deionized water source 342 to flush out themanifold 332 in addition to, or in place of non-reactive gas.Electrolyte from the electrolyte sources 304 may also be utilized as apurge medium.

[0027] A second gas delivery line 352 is teed between the first gasdelivery line 350 and the dosing pump 312. A purge fluid includes atleast one of the electrolyte, deionized water or non-reactive gas fromtheir respective sources 304, 342, 344 may be diverted from the firstdelivery line 350 through the second gas delivery line 352 to the dosingpump 312. The purge fluid is driven through the dosing pump 312 and outthe output line 340 to the manifold 332. The valve bank 334 typicallydirects the purge fluid out a drain port 338 to the reclaimation system232. The various other valves, regulators and other flow control devisesfor not been described and/or shown for the sake of brevity.

[0028] In one embodiment of the invention, a first chemistry may beprovided to the manifold 332 that promotes feature filling of copper ona semiconductor substrate. The first chemistry may include between about2 and about 20 g/l of copper, between about 20 and about 100 ppm ofchlorine, and between about 0.1 and about 5 g/l of acid. As the firstchemistry generally does not completely fill the feature and has aninherently slow deposition rate, the first chemistry may be optimized toenhance the defect ratio of the deposited layer. In another embodiment,the first chemistry generally includes between about 30 and about 65 g/lof copper, between about 15 and about 100 ppm of chlorine, between about5 and about 50 g/l of acid, between about 4 and about 100 ppm (ormilligram per liter) of accelerator, between about 50 and 1000 ppm ofsuppressor, and no leveler. The first chemistry is delivered from themanifold 332 to a first plating cell 102 to enable features disposed onthe substrate to be substantially filled with metal. A second chemistrymay be provided to another plating cell on system 100 via manifold 332,wherein the second chemistry is configured to promote planar bulkdeposition of copper on a substrate. The second chemistry may includebetween about 20 and about 70 g/l of copper, between about 15 and about100 ppm of chlorine and between about 10 and about 100 g/l of acid, forexample. In a specific embodiment, the second chemistry may includebetween about 30 and about 60 g/l of copper, between about 20 and about80 ppm of chlorine, between about 10 and about 50 g/l of acid, betweenabout 4 and about 100 ppm of accelerator, between about 50 and about1000 ppm of suppressor, and between about 6 and about 10 ml/L (or theequivalent ppm) of leveler. The second chemistry is delivered from themanifold 332 to the second process cell to enable an efficient bulkmetal deposition process to be performed over the metal deposited duringthe feature fill deposition step to fill the remaining portion of thefeature. Since the second chemistry generally fills the upper portion ofthe features, the second chemistry may be optimized to enhance theplanarization of the deposited material without substantially impactingsubstrate throughput. Thus, the two step different chemistry depositionprocess allows for both rapid deposition and good planarity of depositedfilms to be realized.

[0029] When utilized with a process cell requiring anolyte solutions,the plating solution delivery system 111 may generally include ananolyte fluid circuit 380 that is coupled to the inlet 209 of theplating cell 200. The anolyte fluid circuit 380 may include a pluralityof additive sources 382 coupled by a dosing pump 384 to a manifold 386that directs additives (typically not utilized) selectively metered fromone or more of the sources 382 and combined with an anolyte in themanifold 386 to those process cells (such as the cell 200) requiringanolyte solution during the plating process. The anolyte may be providedby an anolyte source 388.

[0030] Embodiments of the invention generally provide a method forplating metal onto a substrate. Various embodiments of the method aredescribed in detail below. The embodiments of the invention generallyinclude a multiple chemistry or solution plating process. For example,the embodiments described herein generally include plating a metal froma first solution onto the substrate and plating a metal from a secondsolution, having a different chemistry than the first solution, onto thesubstrate. As used herein, the terms chemistry and solution (which areused interchangeably) are intended to generally represent a fluidsolution and the accompanying additives used to conduct anelectrochemical plating process.

[0031] The process is described herein in terms of copper, but it willbe known to those skilled in the art that any metals and metal alloysused for semiconductor processing, such as tungsten, nickel, cobalt,silver, ruthenium, titanium, titanium nitride, and other similar metalscan be used in embodiments of the invention. The process generallyincludes depositing a barrier layer, such as tantalum nitride, tungstennitride, cobalt, and/or ruthenium over a patterned dielectric material,such as silicon dioxide, deposited on the surface of the substrate. Thebarrier layer generally prevents the migration of copper (or otheroverlying materials) into the dielectric material. Many techniques knownto one skilled in the art, such as physical vapor deposition (PVD),chemical vapor deposition (CVD), atomic layer deposition (ALD), orelectroless plating, for example, can be used to deposit the barrierlayer. Generally, the barrier layer has a thickness of between about 100Å and about 300 Å.

[0032] The first and second plating chemistries or solutions generallyinclude copper sulfate and other copper salts, such as copperfluoborate, copper gluconate, copper sulfamate, copper sulfonate, copperpyrophosphate, copper chloride, or copper cyanide. Additionally, thefirst and second solutions generally include an acid in an amountsufficient to adjust the pH of the solution to a desired level for theparticular plating process. Acids typically used in electrochemicalplating chemistries generally include sulfuric acid, phosphoric acid,and/or derivatives thereof. Additionally, the first and second solutionsmay include halide ions, such as chlorine and/or bromine, for example.

[0033] The first and second solutions can further include platingsolution additives, generally organics, which aid in controlling theplating characteristics of the copper ions onto the substrate and intothe features. For example, the additives can include suppressors, whichadsorb on the surface of the substrate to slow down copper deposition inthe adsorbed area. The suppressors may include any organic substancethat will slow down metal deposition on the substrate or reducecorrosion of the deposited metal under otherwise identical conditions.The suppressors are generally organic oxides or glycol ethers having amolecular weight of greater than about 500. Preferably, the suppressorshave a molecular weight of between about 1000 and about 10000. Forexample, the suppressor may include copolymers of ethylene oxide andpropylene oxide, polyethylene glycol, polypropylene glycol, and glycolethers. The suppressors are commercially available from many suppliers,such as chemicals supplied by BASF Chemicals of Mt. Olive, N.J. underthe trade names Pluronic and Tetronic. The additives may further includeaccelerators, which generally compete with suppressors for adsorptionsites on the substrate surface, accelerating the copper deposition inadsorbed areas. Accelerators generally includes sulfides or disulfides,such as mercapto-propyl-sulphide (MPS) and bis(3-sulfopropyl) disulfide.Preferably, the accelerator includes sulfopropyl disulfides (SPS). Theadditives may further include leveling agents configured to minimizelocalized heavy deposits of metal, e.g., metal over the narrow features.Additionally, the leveling agent is configured to reduce copper growthat the edge of features, thereby providing a smoother metal finish.Levelers generally behave like suppressors, but tend to be moreelectrochemically active (i.e., levelers are generally more easilyelectrochemically transformed) than suppressors typically being consumedduring electroplating. Levelers also tend to accelerate plating ondepressed regions of the surface undergoing plating, thus, tending tolevel the plated surface. Commonly used levelers generally includenitrogen-containing compounds, such as derivatives of amines andimidazoles. Other levelers include 2,4-imidazolidine-diol,thiohydantoin, polyethers, polysulfides, and various dyes. The additivesmay further include surface wetting agents, anti-foaming agents or otheroxygen-reduction agents.

[0034] In one embodiment of the invention, the first solution isgenerally configured to deposit a barrier coverage layer from the firstsolution onto a barrier layer. Direct plating on barrier layers, such ascobalt, for example, presents several challenges. However, plating onbarrier layer is desirable, as this process eliminates the requirementfor depositing a seed layer on the substrate, and thus, reduces the costper substrate. With regard to the challenges associated with plating onbarrier layers, in direct plating on a barrier layer the electrolyte andapplied current density combination must be carefully configured suchthat the substrate metal or barrier layer is well protected during theelectrodeposition process. Additionally, the electrolyte and currentdensity combination should be configured to promote adequate adhesionbetween the substrate metal and the deposited layer. Further, in directplating on barrier layer applications a very thin 3rd metal layer maybeneeded between the substrate and the deposition layer of interest inorder to further facilitate adhesion. Once the layer is plated on thebarrier layer, a second plating solution is generally configured todeposit a layer over the barrier coverage layer and to fill the featuresformed on the substrate or into a layer formed on the substrate. Thesecond solution generally includes copper sulfate at a concentration ofbetween about 20 g/L and about 50 g/L, and halide ions (such as chlorineions) at a concentration of between about 10 ppm and about 100 ppm. Thesecond solution further includes one or more suppressors. Preferably,the second solution includes suppressors in a concentration greater thanthe saturation suppression limit, e.g., the concentration where themetal deposition would not be further suppressed with additionalsuppressors. The suppressor concentration in the second solutiongenerally depends upon the individual system requirements and thesuppressor used, but is generally between about 10 ppm and about 20,000ppm. Additionally, the second solution generally includes an acid at aconcentration of between about 5 g/L and about 100 g/L, or morespecifically, between about 5 and about 10 g/L, resulting in a secondsolution pH of between about 0.6 and about 3.

[0035] In another embodiment of the invention, a copper seed layer isdeposited on the barrier layer using conventional methods, such as PVD,CVD, or ALD, to improve adhesion between a subsequently deposited metallayer and the substrate/barrier layer. The seed layer generally has athickness of between about 50 Å and about 1500 Å, depending on theaspect ratio of the features. In many embodiments the seed layer may bebetween about 50 and about 500 Å thick. One advantage of the currentinvention is that the thin seed layer need not have uniform coverageover the barrier layer in order to support uniform plating thereover insubsequent plating processes. To enable the use of very thin seedlayers, or seed layers having such non-uniformity, the substrate isplated to form a thin film layer thereon, with the features thereof arefilled in a continuous, multiple chemistry deposition process.

[0036] When the seed layer is continuous, but very thin, the resistanceof the seed layer is generally higher than the resistance of a thickerseed layer, e.g., a seed layer having a thickness of greater than about500 Å. As a result, the resistance of a thin seed layer can be higherthan the resistance of traditional plating solutions, thereby causing aflux differentiation in the plating process that generally results in anedge high layer, i.e., a layer that is thicker near the perimeter of acircular substrate. Accordingly, in one embodiment of the invention, thefirst plating solution includes a low Cu and low acid concentration,e.g., between about 2 and about 20 g/L Cu, and between about 0.1 andabout 5 g/l acid, which results in a first solution resistance ofbetween about 40 ohm cm and about 200 ohm cm (e.g., a resistance that isgenerally higher than the seed layer resistance). Accordingly, in oneembodiment of the invention, the first plating solution includes a lowchlorine concentration that is configured to increase the bathresistance in order to compensate for the edge high deposition thatinherently results when thin seed layers are used. The bath electricalresistivity of acidic CuSO₄ bath is generally determined by the acidconcentration of the bath, followed by the CuSO₄ concentration. Loweringthe acidity from between about 30 and about 50 g/l to about 0.1 to about1 g/l, and lowering the CuSO₄ concentration from about 30 to about 70g/l to about 2 to about 20 g/l will greatly increase the bathresistivity, and therefore, facilitate plating on a very thin seedlayer. As an example, the resistivity for 50 g/l Cu (as CuSO₄)+30 g/lH₂SO₄ is about 10 ohm cm, while the resistivity for 5 g/l Cu+0.2 g/lH₂SO₄ is increased to about 130 ohm cm, which is greater than a 10 timesincrease in resistivity of the bath. As a result of the increasedresistance, the metal ions plate from the solution onto the very thinseed layer very slowly, resulting in improved control over the platingprocess and the ability to plate on a very thin, possibly discontinuous,seed layer.

[0037] When the seed layer includes non-uniformities, the first solutiongenerally includes copper sulfate at a concentration of between about 2g/L and about 50 g/L. Preferably, the first solution includes coppersulfate at a concentration of less than about 20 g/L. Additionally, thefirst solution may include sulfuric acid at a concentration of betweenabout 0.1 g/L and about 1 g/L, resulting in a first solution pH ofbetween about 1 and about 4. More preferably, the first solution pH isbetween about 2 and about 3. Additionally, the first solution alsoincludes halide ions, such as chlorine, at a concentration of betweenabout 20 ppm and about 100 ppm. Additionally, the first solution mayinclude oxygen reducing agents to limit copper corrosion rate.

[0038] The first solution further includes one or more suppressors in aconcentration greater than the saturation suppression limit, e.g., theconcentration where the metal deposition would not be further suppressedwith additional suppressors. The suppressor concentration in the firstsolution generally depends upon the individual system requirements andthe suppressor used, but is generally between about 100 ppm and about10,000 ppm. The seed layer is exposed to the first solution under anapplied first current, generally having a current density applied to thesurface of the substrate of less than about 5 mA/cm², or the currentdensity may be less than about 3 mA/cm², however, embodiments of theinvention are not limited to current densities lower than 5 mA/cm². Thesubstrate is then subjected to further copper deposition, whereby thecopper deposition is essentially continuous, but the plating solution ismodified, e.g., a second solution provides the metal ions to thesubstrate. As used herein, “continuous” can include a minimal platingstoppage, e.g., a pause in plating while either the plating solution isbeing replaced or while the substrate is being transferred to anotherplating cell. Generally, a current density of less than about 10 mA/cm²is applied to the second solution to urge the metal ions out of thesecond solution and into the features. Preferably, the current densityis less than about 5 mA/cm². The second solution generally includes thesame components as the first solution, plus an accelerator. Therefore,the second solution can be used in conjunction with the first solutionwithout significant variations in the design of the plating cell andplating conditions. The accelerator generally competes with thesuppressors for adsorption sites, accelerating the copper deposition inadsorbed areas. The accelerator generally includes sulfides ordisulfides, such as mercapto-propyl sulphide (MPS) andbis(3-sulfopropyl) disulfide. Preferably the accelerator includessulfopropyl disulfides (SPS). The first solution, which is acidic, isgenerally configured to plate a metal, generally copper, onto a thin andsometime noncontiguous seed layer. Thus, the first solution is generallyconfigured to plate with minimal defects at a relatively slow platingrate so that the layer generated by the first solution adequately coversthe underlying seed layer and does not contain any discontinuities.

[0039] The second solution generally includes an acid at a concentrationof between about 5 g/L and about 10 g/L, resulting in a pH of betweenabout 0.6 and about 3. The second solution may also contain variousconcentrations of the above noted additives (levelers, suppressors,accelerators, and copper corrosion inhibitors, such as benzotriazole andother amine, amino derivatives, etc). The second solution may generallybe configured to plate either a feature fill layer over a layer platedon a thin seed layer or a bulk fill layer over a layer plated over anormal thickness seed layer. In the instance where the second solutionis plating over a layer that is plated on a thin seed layer, the secondsolution is generally configured to provide good feature fill, minimaldefects, and relatively fast plating rates from the acidic bath.

[0040] In another embodiment of the invention, the plating processincludes plating a metal alloy on the substrate. The alloy may be platedonto the surface of the substrate in order to reduce stress migration,improve electromigration characteristics, and/or increase adhesionbetween an overlying fill layer and the underlying layer, which may be aseed layer or other layer. For example, the first solution can includecopper sulfate, as described above, while the second solution includes acopper alloy solution rather than copper sulfate. Alternatively, thefirst solution can include the copper alloy solution and the secondsolution can include copper sulfate, or both the first and secondsolution can include copper alloys. Generally, the alloy included in thesolution is the same metal as either the seed layer or the barrier layermaterial upon which the first solution is contacting, which facilitatesadhesion between the respective layers. Regardless of the order of theparticular chemistries, the process is generally configured to plate analloy and/or a metal from a first chemistry, and then plate an alloy ora metal from a second bath.

[0041] Additionally, the first solution may include an anti-foamingagent to reduce foam on the surface of the solution at the outset ofplating, e.g., initial application of current. The foam that oftenresults in plating solutions is generally the result of agitation of theplating solution by the plating processes, i.e., insertion, removal, anrotation of a substrate support or head assembly in the platingsolution. Since the foam itself may contain contaminants or otherwiseconcentrate elements that are not favorable to plating processes, it isdesirable to minimize or eliminate the foam that forms on top of thebaths, as the contaminants and/or undesirable elements that form on thefoam have been shown to increase plating defects. There are generallythree types of surfactants that can be used as effective wetting agentsin semiconductor processing applications. For example, anionicsurfactants are generally sulfonic acids or thiols with long hydrocarbonchains of greater than 16 carbon atoms; cationic surfactants are ingeneral amine or amino acids with long hydrocarbon chains; and non-ionicsurfactants like alcohols and glycols with long enough hydrophobichydrocarbon chains such as octanol and all the suppressors we mentionedin the application. Additional exemplary antifoaming agents includehydrophobic oil, compounds with surfactants or surfactant mixtures thathave limited solubility in aqueous mixtures, and ethanol solutions. Theanti-foaming agent generally operates to reduce defects formed in theinitial metal film. However, generally the foam that forms on thesurface of electrochemical plating baths is most detrimental only to theinitial plating process, i.e., the plating of the initial layer. Assuch, since antifoaming agents may have some adverse effect on otherplating parameters, a first solution may include an antifoaming agentand a second solution may be configured to plate a layer over a layerformed in the first solution. This method allows for a first layer to beformed with minimal defects, as the foam is reduced, and then thesubstrate may be further plated in a second solution without theantifoaming solution.

[0042] Additionally, each of the plating processes described herein mayfurther include as an intermediate step the plating process associatedwith the first solution and the plating process associated with thesecond solution, rinsing the substrate surface to remove any localizedconcentrations of additives, such as suppressors, on the surface of thesubstrate, as these concentrations may adversely affect the subsequentplating process in the next chemistry. Preferably, this rinsing isprovided by passing a solution including pure deionized water, e.g.,deionized water including less than about 1 ppm of chlorides and noorganic compounds, over the substrate.

[0043] Another embodiment of the invention may be utilized to ensurethat features are adequately filled in preceding plating processes.Inherently, the filling of each and every feature on a substrate may notoccur simultaneously or in the same time frame. Therefore, embodimentsof the invention may further include plating a substrate with a thirdsolution to form an overburden layer and ensure that all of the featureshave been adequately filled. The overburden step generally includescontacting the deposited metal with a third solution under an appliedcurrent density of at least 10 mA/cm², and generally the current densityis greater than about 30 mA/cm², which is permissible because, the loweror deeper regions of the features will already be filled and the highercurrent density at this stage will not cause closure of the openings ofhigh aspect ratio features. The third solution generally includes thecomponents of the second solution used in the plating process, asdescribed above and, in addition, one or more leveling agents, whichhave been described above.

[0044] In operation, the individual plating solutions can be supplied tothe plating cell by flushing or rinsing. For example, the first solutionmay be rinsed from the plating cell and the second plating solution maybe flowed into the plating cell, preferably with deionized water, toprovide continuous metal deposition to the substrate. In anotherembodiment, the above-described process generally is carried out inseparate processing cells located on the same platform, e.g., eachsolution is used in a separate cell in communication with additionalplating cells, although other plating platforms can be utilized. Byutilizing separate processing cells, the individual solutions aretailored to meet the different needs required by each step, therebyimproving the resultant metal layer. For example, the second solutiongenerally provides bottom-up fill of the features, but results inmounding of the narrow features if used past the filling of the narrowfeatures. Therefore, once the narrow features have been filled, a thirdsolution is utilized to ensure a smooth finish and enabling subsequentprocessing steps. As a result of the individual solutions and solutionrequirements, solution supplies of less than about 15 mL are possible,thereby facilitating the complete disposal and replacement of thesolutions when necessary.

[0045] While the foregoing is directed to embodiments of the presentinvention, other and further embodiments of the invention can be devisedwithout departing from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A method for plating metal onto a substrate,comprising: forming a metal layer in the features by plating metal ionsfrom a first solution in features formed into the substrate under afirst applied current density, wherein the first solution comprises anacid in an amount sufficient to provide a first solution pH of less thanabout 6, copper ions, and at least one suppressor; and substantiallyfilling the features by plating metal ions from a second solution in thefeatures under a second applied current density, wherein the secondsolution comprises an acid in an amount sufficient to provide a secondsolution pH of between about 0.6 and about 4, copper ions, at least onesuppressor and at least one accelerator.
 2. The method of claim 1,further comprising forming the metal layer on a metal seed layer formedon the surface of the substrate.
 3. The method of claim 2, wherein themetal seed layer has a thickness of between about 50 Å and about 1500 Å.4. The method of claim 3, wherein the metal seed layer is discontinuous.5. The method of claim 3, wherein the metal seed layer is continuous 6.The method of claim 2 wherein the first solution has a resistance thatis greater than a resistance of the seed layer.
 7. The method of claim1, wherein the first applied current density is between about 0.5 mA/cm²and about 5 mA/cm².
 8. The method of claim 1, wherein the first appliedcurrent density is between about 0.5 mA/cm² and about 3 mA/cm².
 9. Themethod of claim 1, wherein the first solution comprises copper sulfatein a concentration of between about 2 g/L and about 50 g/L.
 10. Themethod of claim 1, wherein the first solution comprises copper sulfatein a concentration of between about 2 g/L and about 20 g/L.
 11. Themethod of claim 1, wherein the second solution comprises a copper alloysolution.
 12. The method of claim 1, wherein the first solutioncomprises a copper alloy.
 13. The method of claim 12, wherein the secondsolution comprises copper sulfate.
 14. The method of claim 12, whereinthe second solution comprises a copper alloy.
 15. The method of claim 1,wherein the first solution pH is between about 1 and about
 4. 16. Themethod of claim 1, wherein the first solution pH is between about 2 andabout
 3. 17. The method of claim 1, wherein the first solution furthercomprises chlorine ions in a concentration of between about 10 ppm andabout 100 ppm.
 18. The method of claim 1, wherein each of the one ormore suppressors have a molecular weight of greater than about
 500. 19.The method of claim 1, wherein each of the one or more suppressors havea molecular weight of between about 1000 and about 10,000.
 20. Themethod of claim 1, further comprising rinsing the substrate surface witha deionized water rinsing solution.
 21. The method of claim 20, whereinthe rinsing solution comprises deionized water and chlorine in aconcentration of less than about 1 ppm.
 22. The method of claim 1,further comprising forming the metal layer on a copper barrier layerformed on the surface of the substrate.
 23. A method for depositing ametal on a substrate having features and field areas, comprising:substantially filling the features by plating metal ions from a firstsolution in the features under a first applied current, wherein thefirst plating solution comprises an acid in an amount sufficient toprovide a first solution pH of from about 0.6 to about 3, copper ions,and at least one suppressor and at least one accelerator; and growing afilm layer on the field areas by plating metal ions from a secondplating solution under a second applied current to form a metal layer onthe substrate, wherein the second plating solution comprises an acid,copper ions, at least one suppressor, at least one accelerator and atleast one leveling agent and wherein the second applied current has acurrent density that is greater than a current density of the firstapplied current.
 24. The method of claim 23, wherein the first platingsolution comprises sulfuric acid in a concentration of from about 5 g/Lto about 10 g/L.
 25. The method of claim 23, wherein the first appliedcurrent has a current density of between about 0.5 mA/cm² about 5mA/cm².
 26. The method of claim 23, wherein the second applied currenthas a current density of greater than about 30 mA/cm².
 27. A method forplating metal onto a substrate, comprising: depositing a metal seedlayer on the surface of the substrate, the surface comprising fieldareas and features; substantially filling the features by plating ametal from a first solution onto the metal seed layer to form a firstfill layer, wherein the first solution comprises an acid in an amountsufficient to provide a first solution pH of between about 0.5 and about6, copper ions, and at least one suppressor; substantially fillingfeatures on the substrate by plating metal ions from a second solutiononto the first fill layer to form a second fill layer, wherein thesecond solution comprises an acid in an amount sufficient to provide asecond solution pH of from about 0.6 to about 3, copper ions, at leastone suppressor, and at least one accelerator; and growing a film layeron the field areas by contacting the second fill layer with a thirdsolution, wherein the third solution comprises an acid, copper ions, atleast one suppressor, at least one accelerator, and at least oneleveling agent.
 28. A first plating solution for plating metal on ametal seed layer, comprising: copper sulfate in a concentration ofbetween about 5 g/L and about 50 g/L; sulfuric acid in a concentrationsufficient to provide a pH of between about 0.5 and 6; and suppressorshaving a molecular weight of greater than about 500.